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Abstract:

One exemplary embodiment can be a process for alkylating benzene. The
process can include obtaining at least a portion of a stream from a
transalkylation zone, combining the at least the portion of the stream
from the transalkylation zone with a fuel gas stream, and providing at
least a portion of the combined stream to a benzene methylation zone.
Typically, the fuel gas stream includes an effective amount of one or
more alkanes for alkylating at least partially from a hydrogen
purification process tail gas.

Claims:

1. A process for alkylating benzene, comprising: A) obtaining at least a
portion of a stream from a transalkylation zone; B) combining the at
least the portion of the stream from the transalkylation zone with a fuel
gas stream comprising an effective amount of one or more alkanes for
alkylating at least partially from a hydrogen purification process tail
gas; and C) providing at least a portion of the combined stream to a
benzene methylation zone.

2. The process according to claim 1, further comprising a sponge
absorption zone receiving the combined stream and a stream comprising
benzene, and providing an effluent to the benzene methylation zone.

3. The process according to claim 1, further comprising obtaining a
stream comprising benzene from a fractionation zone.

4. The process according to claim 1, further comprising providing an
effluent from the transalkylation zone to a stripper zone.

5. The process according to claim 4, wherein the at least the portion of
the stream from the transalkylation zone is obtained from the stripper
zone.

6. The process according to claim 1, wherein the fuel gas stream
comprises at least about 8%, by mole, of one or more C3.sup.+
hydrocarbons.

7. The process according to claim 3, providing a product stream
comprising one or more aromatics from an extraction zone to the
fractionation zone.

9. The process according to claim 3, wherein the fractionation zone
provides a stream comprising toluene.

10. The process according to claim 1, wherein the benzene methylation
zone operates at a temperature of about 250- about 700.degree. C., a
pressure of about 100- about 21,000 kPa, and a hydrogen:hydrocarbon mole
ratio of about 0.1:1- about 5:1.

11. The process according to claim 10, wherein the benzene methylation
zone comprises a catalyst, wherein the catalyst comprises a molecular
sieve.

12. The process according to claim 7, wherein a bottom stream from the
fractionation zone comprises para-xylene; and further processing the
product stream for manufacturing at least one of polyethylene
terephthalate and purified terephthalic acid.

13. A process for alkylating benzene, comprising: A) providing at least a
portion of a stream from a transalkylation zone to a first or a second
benzene methylation zone; B) providing a feed comprising one or more
C4.sup.+ hydrocarbons to the first benzene methylation zone; and C)
combining at least a portion of an effluent comprising an effective
amount of one or more alkanes for alkylating from a hydrogen purification
process with at least a portion of an effluent comprising one or more
C4.sup.- hydrocarbons from the first benzene methylation zone to the
second benzene methylation zone.

14. The process according to claim 13, wherein the second benzene
methylation zone operates at a temperature of about 10- about 100.degree.
C. higher than the first benzene methylation zone.

15. The process according to claim 13, further comprising providing an
effluent from the transalkylation zone to a stripper zone, and in turn,
providing an overhead stream from the stripper zone to a sponge
absorption zone.

16. The process according to claim 15, further comprising combining the
overhead stream and a fuel gas stream comprising the effective amount of
one or more alkanes for alkylating from a hydrogen purification process
tail gas.

17. The process according to claim 16, wherein the fuel gas stream
comprises at least about 8%, by mole, one or more C3.sup.+ hydrocarbons.

18. The process according to claim 16, wherein the fuel gas stream is
obtained from a pressure swing adsorber.

19. The process according to claim 13, wherein the first and second
benzene methylation zones operate, independently, at a temperature of
about 250- about 700.degree. C., a pressure of about 100- about 21,000
kPa, and a hydrogen:hydrocarbon mole ratio of about 0.1:1- about 5:1.

20. A process for alkylating benzene, comprising: providing at least a
portion of a stream comprising one or more C3.sup.+ hydrocarbons from a
sponge absorption zone to a benzene methylation zone wherein the benzene
methylation zone operates at a temperature of about 250- about
700.degree. C. and a pressure of about 100- about 21,000 kPa for
producing one or more xylenes.

Description:

FIELD OF THE INVENTION

[0001] The present invention generally relates to a process for alkylating
benzene.

DESCRIPTION OF THE RELATED ART

[0002] Typically, an aromatic complex can process a hydrotreated naphtha
feed to produce various products such as benzene and one or more xylenes.
However, it may be desirable to produce higher substituted aromatics
depending, e.g., on market conditions. In addition, when producing motor
fuel products, increasingly stringent environmental regulations can
require lower benzene content. As a consequence, there is a demand for
alternative processes for removing benzene from, e.g., gasoline. Thus,
systems and processes that allow flexibility to convert benzene to other
and higher valued products may be desirable.

[0003] However, existing processes can use expensive catalysts and/or
reactants that can require further processing to separate undesirable
by-products. Thus, it would be advantageous to provide an agent that can
convert benzene to other substituted aromatics while minimizing
undesirable products and/or side reactions.

[0004] One exemplary technology can methylate benzene using an alkylating
agent from any suitable source. The alkylating agent can be obtained from
an aromatic extraction raffinate and/or a light naphtha. In such a
process, a significant portion of the raffinate and light naphtha can be
converted to propane.

[0005] However, such processes have several disadvantages. It would be
beneficial to identify and utilize other sources within a refinery or
chemical manufacturing complex for providing the suitable alkylating
agent. In addition, often only a single benzene methylation stage is
utilized, which can suffer insufficient selectivity for producing the
desired alkylate. As a consequence, there is a desire to provide
flexibility and efficiency within an aromatic complex when utilizing
refinery or chemical manufacturing streams for producing alkylates.

SUMMARY OF THE INVENTION

[0006] One exemplary embodiment can be a process for alkylating benzene.
The process can include obtaining at least a portion of a stream from a
transalkylation zone, combining the at least the portion of the stream
from the transalkylation zone with a fuel gas stream, and providing at
least a portion of the combined stream to a benzene methylation zone.
Typically, the fuel gas stream includes an effective amount of one or
more alkanes for alkylating at least partially from a hydrogen
purification process tail gas.

[0007] Another exemplary embodiment may be a process for alkylating
benzene. The process can include providing at least a portion of a stream
from a transalkylation zone to a first or a second benzene methylation
zone, providing a feed including one or more C4.sup.+ hydrocarbons to the
first benzene methylation zone, and combining at least a portion of an
effluent including an effective amount of one or more alkanes for
alkylating from a hydrogen purification process with at least a portion
of an effluent including one or more C4.sup.- hydrocarbons from the first
benzene methylation zone to the second benzene methylation zone.

[0008] Yet another exemplary embodiment can be a process for alkylating
benzene. Generally, the process includes providing at least a portion of
a stream having one or more C3.sup.+ hydrocarbons from a sponge
absorption zone to a benzene methylation zone. Usually, the benzene
methylation zone operates at a temperature of about 250- about
700° C. and a pressure of about 100- about 21,000 kPa for
producing one or more xylenes.

[0009] The embodiments provided herein can utilize at least a portion of
various streams, such as a fuel gas stream from a hydrogen purification
process tail gas or a raffinate stream from a transalkylation zone to
provide a suitable alkylating agent for benzene. Generally, it is
preferred that the alkylating agent methylates benzene to form one or
more xylenes. Usually, a benzene methylation zone along with an optional
sponge adsorption zone can be added to an aromatic apparatus for
improving aromatic alkylation. In one exemplary embodiment, a plurality
of benzene methylation zones can be utilized to further enhance
selectivity.

DEFINITIONS

[0010] As used herein, the term "zone" can refer to an area including one
or more equipment items and/or one or more sub-zones. Equipment items can
include one or more reactors or reactor vessels, heaters, separators,
exchangers, pipes, pumps, compressors, and controllers. Additionally, an
equipment item, such as a reactor or vessel, can further include one or
more zones or sub-zones.

[0011] As used herein, the term "stream" can be a stream including various
hydrocarbon molecules, such as straight-chain, branched, or cyclic
alkanes, alkenes, alkadienes, and alkynes, and optionally other
substances, such as gases, e.g., hydrogen, or impurities, such as heavy
metals. The stream can also include aromatic and non-aromatic
hydrocarbons. Moreover, the hydrocarbon molecules may be abbreviated C1,
C2, C3 . . . Cn where "n" represents the number of carbon atoms in the
hydrocarbon molecule and be further characterized by a superscript "+" or
"-" symbol. In such an instance, a stream characterized, e.g., as
containing C3.sup.-, can include hydrocarbons of three carbon atoms or
less, such as one or more compounds having three carbon atoms, two carbon
atoms, and/or one carbon atom. Also, the symbol "A" in conjunction with a
numeral and/or a superscript plus or minus may be used below to represent
one or more aromatic compounds. As an example, the abbreviation "A9" may
represent one or more aromatic C9 hydrocarbons.

[0012] As used herein, the term "aromatic" can mean a group containing one
or more rings of unsaturated cyclic carbon radicals where one or more of
the carbon radicals can be replaced by one or more non-carbon radicals.
An exemplary aromatic compound is benzene having a C6 ring containing
three double bonds. Moreover, characterizing a stream or zone as
"aromatic" can imply one or more different aromatic compounds.

[0013] As used herein, the term "rich" can mean an amount generally of at
least about 50%, and preferably about 70%, by weight, of a compound or
class of compounds in a stream.

[0014] As used herein, the term "substantially" can mean an amount
generally of at least about 90%, preferably about 95%, and optimally
about 99%, by weight, of a compound or class of compounds in a stream.

[0015] As used herein, the term "selectivity" can be calculated as weight
percent of converted alkanes that become A7.sup.+ alkyl groups based on
the total alkanes in a reaction feed. Similarly, selectivity of alkanes
in a fuel gas, e.g., C1-C4 hydrocarbons, can be the weight percent of
alkanes converted to A7.sup.+ alkyl groups and fuel gas compounds, such
as methane and ethane.

[0016] As depicted, process flow lines in the figures can be referred to
interchangeably as, e.g., lines, pipes, feeds, effluents, products, or
streams.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic depiction of an aromatic production
apparatus.

[0018]FIG. 2 is a schematic depiction of another exemplary aromatic
production apparatus.

DETAILED DESCRIPTION

[0019] Referring to FIG. 1, an aromatic production apparatus 100 can
include an extraction zone 150, a transalkylation zone 180, a stripper
zone 200, a fractionation zone 220, a sponge adsorption zone 250, and a
benzene methylation zone 270. Typically, the aromatic production
apparatus 100 is part of a refinery or chemical manufacturing facility
and produces a desired xylene, such as para-xylene or meta-xylene.

[0020] Generally, the extraction zone 150 can receive a reformate feed
104, including one or more C7.sup.- hydrocarbons. The reformate feed 104
can be obtained from an overhead stream of a reformate splitter
distillation column, which in turn may be obtained from a reforming zone
that converts paraffins and naphthenes into one or more aromatic
compounds. Typically, a reforming zone can operate at very high severity
and produce about 100- about 106 research octane number gasoline
reformate in order to maximize the production of one or more aromatic
compounds. Generally, a hydrocarbon stream, typically a naphtha, is
contacted with a reforming catalyst under reforming conditions. Such a
reforming zone is disclosed in, e.g., U.S. application Ser. No.
12/689,751 filed Jan. 19, 2010.

[0021] The extraction zone 150 can utilize an extraction process, such as
extractive distillation, liquid-liquid extraction or a combined
liquid-liquid extraction/extractive distillation process. An exemplary
extraction process is disclosed in Thomas J. Stoodt et al., "UOP
Sulfolane Process", Handbook of Petroleum Refining Processes, McGraw-Hill
(Robert A. Meyers, 3rd Ed., 2004), pp. 2.13-2.23. Preferably, extractive
distillation is utilized, which can include at least one column known as
a main distillation column and may comprise a second column known as a
recovery column.

[0022] Extractive distillation can separate components having nearly equal
volatility and having nearly the same boiling point. Typically, a solvent
is introduced into a main extractive-distillation column above the entry
point of the hydrocarbon stream being extracted. The solvent may affect
the volatility of the components of the hydrocarbon stream boiling at
different temperatures to facilitate their separation. Exemplary solvents
include tetrahydrothiophene 1,1-dioxide, i.e. sulfolane,
n-formylmorpholine, i.e., NFM, n-methylpyrrolidinone, i.e., NMP,
diethylene glycol, triethylene glycol, tetraethylene glycol, methoxy
triethylene glycol, or a mixture thereof. Other glycol ethers may also be
suitable solvents alone or in combination with those listed above.

[0023] The extraction zone 150 can produce a product stream 156 including
one or more aromatic compounds, typically benzene and toluene, and a
raffinate stream 158. Generally, the raffinate stream 158 can be sent
outside the aromatic production apparatus 100 and utilized in any
suitable process in the refinery or chemical manufacturing facility. In
an alternative embodiment, the raffinate stream 158 may be provided to
the benzene methylation zone 270.

[0024] The product stream 156 including one or more aromatics can be
combined with a stripper bottom stream 208, as hereinafter described, to
form a combined feed 212 to the fractionation zone 220. The fractionation
zone 220 can include a benzene fractionation zone 230 and a toluene
fractionation zone 240. Generally, the benzene fractionation zone 230 can
include a distillation column that provides an overhead stream 232
including benzene and a bottom stream 234 including one or more A7.sup.+
compounds. This bottom stream 234 can be provided as a feed to the
toluene fractionation zone 240, which may include a distillation column
and provide an overhead stream 244 including toluene and a bottom stream
246 including one or more A8.sup.+ aromatics.

[0025] Usually, the bottom stream 246 can include any suitable amount of
compounds, namely A8.sup.+ compounds that can be used to manufacture
xylenes. Typically, the bottom stream 246 can be provided to a
para-xylene separation zone and isomerization zone as disclosed in, e.g.,
U.S. Pat. No. 7,727,490, for producing desired aromatics, such as
para-xylene or meta-xylene. A product stream including para-xylene may be
used as a feedstock in a process to manufacture, e.g., at least one of
polyethylene terephthalate and purified terephthalic acid. The overhead
stream 244 can be sent to the transalkylation zone 180.

[0026] Although not wanting to be bound by any theory, at least two
reactions, namely, disproportionation and transalkylation can occur in
the transalkylation zone 180. The disproportionation reaction can include
reacting two toluene molecules to form benzene and a xylene molecule, and
the transalkylation reaction can react toluene and an aromatic C9
hydrocarbon to form two xylene molecules. As an example with respect to
the transalkylation reaction, a reactant of one mole of trimethylbenzene
and one mole of toluene can generate two moles of xylene, such as
para-xylene, as a product. The ethyl, propyl, and higher alkyl group
substituted aromatic C9-C10, can convert to lighter single-ring aromatics
via dealkylation. As an example, the methylethylbenzene can lose an ethyl
group through dealkylation to form toluene. Propylbenzene, butylbenzene,
and diethylbenzene can be converted to benzene through dealkylation. The
methyl-substituted aromatics, e.g. toluene, can further convert via
disproportionation or transalkylation to benzene and xylenes. If the feed
to the transalkylation zone 180 has more ethyl, propyl, and higher alkyl
group substituted aromatics, more benzene can be generated in the
transalkylation zone 180. Generally, the ethyl, propyl, and higher alkyl
substituted aromatic compounds have a higher conversion rate than the
methyl-substituted aromatic compounds, such as trimethylbenzene and
tetramethylbenzene.

[0027] In the transalkylation zone 180, the overhead stream 244 may be
contacted with a transalkylation catalyst under transalkylation
conditions. Preferably, the catalyst is a metal stabilized
transalkylation catalyst. Such a catalyst can include a solid-acid
component, a metal component, and an inorganic oxide component. The
solid-acid component typically is a pentasil zeolite, which may include
the structures of MFI, MEL, MTW, MTT and FER (IUPAC Commission on Zeolite
Nomenclature), a beta zeolite, or a mordenite. Desirably, it is a
mordenite zeolite. Other suitable solid-acid components can include
mazzite, NES type zeolite, EU-1, MAPO-36, MAPSO-31, SAPO-5, SAPO-11, and
SAPO-41. Generally, mazzite zeolites include Zeolite Omega. Further
discussion of the Zeolite Omega, and NU-87, EU-1, MAPO-36, MAPSO-31,
SAPO-5, SAPO-11, and SAPO-41 zeolites is provided in, e.g., U.S. Pat. No.
7,169,368 B1.

[0028] Typically, the metal component is a noble metal or base metal. The
noble metal can be a platinum-group metal of platinum, palladium,
rhodium, ruthenium, osmium, or iridium. Generally, the base metal is
rhenium, tin, germanium, lead, cobalt, nickel, indium, gallium, zinc,
uranium, dysprosium, thallium, iron, molybdenum, tungsten, or a mixture.
The base metal may be combined with another base metal, or with a noble
metal. Preferably, the metal component includes rhenium. Suitable metal
amounts in the transalkylation catalyst generally range from about 0.01-
about 10%, preferably range from about 0.1- about 3%, and optimally range
from about 0.1- about 1%, by weight. Suitable zeolite amounts in the
catalyst range from about 1- about 99%, preferably from about 10- about
90%, and optimally from about 25- about 75%, by weight. The balance of
the catalyst can be composed of a refractory binder or matrix that is
optionally utilized to facilitate fabrication, provide strength, and
reduce costs. The binder should be uniform in composition and relatively
refractory. Suitable binders can include inorganic oxides, such as at
least one of alumina, magnesia, zirconia, chromia, titania, boria,
thoria, phosphate, zinc oxide and silica. Preferably, alumina is a
binder. One exemplary transalkylation catalyst is disclosed in, e.g.,
U.S. Pat. No. 5,847,256.

[0029] Usually, the transalkylation zone 180 operates at a temperature of
about 200- about 540° C. and a pressure of about 690- about 4,140
kPa. The transalkylation reaction can be effected over a wide range of
space velocities, with higher space velocities effecting a higher ratio
of para-xylene at the expense of conversion. Generally, the liquid hourly
space velocity is in the range of about 0.1- about 20 hr-1. The
feedstock is preferably transalkylated in the vapor phase and in the
presence of hydrogen. If transalkylated in the liquid phase, then the
presence of hydrogen is optional. If present, free hydrogen can be
associated with the feedstock and recycled hydrocarbons in an amount of
about 0.1- up to about 10 moles, per mole, of an alkylaromatic.

[0030] The transalkylation zone 180 may provide a transalkylation zone
effluent 184. The transalkylation zone effluent 184 can be combined with
a benzene methylation zone effluent 274, as hereinafter described. In an
alternative embodiment, the transalkylation zone effluent 184 may be
provided to the benzene methylation zone 270. The effluents 184 and 274
can form a stripper feed 196. The stripper feed 196 is provided to the
stripper zone 200.

[0031] Generally, the stripper zone 200 includes a stripper column
utilizing any suitable heat source, such as a pressurized steam heat
exchanger or furnace. Usually, the stripper column reboils the liquids
therein to produce a stripper overhead stream 204 and a stripper bottom
stream 208. Generally, the stripper overhead stream 204 can be at least a
portion of the transalkylation zone effluent or stream 184 from the
transalkylation zone 180. The stripper bottom stream 208 can be combined
with the product stream 156 to form the combined feed 212, as described
above.

[0032] The stripper overhead stream 204 can be combined with a fuel gas
stream 112 to form a combined feed 248. Generally, the fuel gas stream
112 can be at least partially obtained from any suitable source, such as
a hydrogen purification process, and include an effective amount of one
or more alkanes. As an example, the fuel gas stream 112 can be obtained
from a tail gas from a hydrogen purification unit, e.g. a pressure swing
adsorber, and from the light ends produce in the transalkylation zone
180. Usually, the fuel gas stream includes one or more C3hydrocarbons and other light non-hydrocarbon gases such as hydrogen, and
typically includes hydrogen, methane, ethane, ethene, and propane. The
fuel gas stream 112 can include at least about 8%, preferably about 10%,
by mole, one or more C3.sup.+ hydrocarbons, such as propane.

[0033] At least a portion of, independently, the streams 112 and 204 can
form a combined feed 248 to the sponge adsorption zone 250. Also, the
overhead stream 232 including benzene may also be provided to the sponge
adsorption zone 250. The sponge adsorption zone 250 can remove C3
hydrocarbons, such as propane, from fuel gas using benzene. Generally,
the sponge adsorption zone 250 can provide a fuel gas stream 254 having a
similar composition as the fuel gas stream 112 minus one or more C3.sup.+
hydrocarbons, and a bottom stream providing at least a portion of a
benzene methylation zone feed 258 including one or more C3 and aromatic
hydrocarbons, typically benzene.

[0034] The sponge adsorption zone 250 can include a tray or packed
absorber or combined packed column-tray absorber, and may be operated at
a preferred temperature of about 6- about 100° C., more preferably
about 10- about 20° C.; and at a pressure of about 0- about 5,000
kPa, preferably about 1,000- about 3,000 kPa. Typically, the absorber
operates in a gas phase and may have from about 5- about 150 distillation
trays. Distillation trays can be valve, sieve, or multiple-downcomer. The
absorber can also be designed with either a random or structured packing
A number of distillation stages provided by the packing can range from
about 4- about 75. The absorber may be constructed from any suitable
material, such as normal carbon steel, and the absorber trays can be
constructed from either carbon or stainless steel. If a packing is used,
it can be either carbon or stainless steel, as disclosed in, e.g., U.S.
Pat. No. 7,238,843 B2.

[0035] The benzene methylation zone feed 258 can be provided to the
benzene methylation zone 270. The benzene methylation zone 270, such as
an alkyl, preferably methyl, can operate under any suitable conditions in
the liquid or gas phase. Particularly, the reaction zone can operate at a
temperature of about 250- about 700° C., preferably about 350-
about 550° C.; a pressure of about 100- about 21,000 kPa,
preferably about 1,900- about 3,500 kPa; a weight hourly space velocity
(WHSV) of about 0.1- about 100 hr-1, preferably about 2- about 10
hr-1; and a hydrogen:hydrocarbon mole ratio of about 0.1:1- about
5:1, preferably about 0.5:1- about 4:1. Sufficient hydrogen may be
present in the fuel gas stream 112, or additional make-up hydrogen may be
provided. The reaction may occur in a gas phase to facilitate the
cracking of non-aromatic hydrocarbons.

[0036] Although not wanting to be bound by theory, it is believed that the
non-aromatic hydrocarbons and/or saturated groups will form methyl groups
instead of alkyl groups. However, it should be understood that at least
some alkylation may be occurring where groups such as, e.g., ethyl,
propyl, butyl, and higher groups, can be substituted to the one or more
aromatic compounds. In an exemplary embodiment, the C3 hydrocarbon
conversion can be about 70%, by weight, per pass. Of the converted C3
hydrocarbon about 30%, by weight, may be converted to the desired product
(A7.sup.+ alkyl group) while the remainder can be converted to fuel gas,
typically C1 and C2 hydrocarbons. Preferably, the conversion of a
substantial portion of the C3 hydrocarbons to fuel gas does not degrade
the value of the stream because typically the feed is a fuel gas stream
as opposed to a petrochemical grade propane. Thus, the functional
selectivity of the alkylating agent to A7.sup.+ aromatics is typically
about 100%, by weight, even when a substantial portion of the C3
hydrocarbon is converted to a lighter product. The unconverted
hydrocarbon C3 can be recycled back to the benzene methylation zone 270
via the transalkylation zone 180. Once through hydrogen is preferred due
to the high methane in recycled hydrogen. Alternatively, a recycle gas
can be purified by any acceptable means such as but not limited to
pressure swing adsorption or a membrane.

[0037] Any suitable catalyst may be utilized such as at least one
molecular sieve including any suitable material, e.g., alumino-silicate.
The catalyst can include an effective amount of the molecular sieve,
which can be a zeolite with at least one pore having a 10 or higher
member ring structure and can have one or higher dimension. Typically,
the zeolite can have a Si/Al2 mole ratio of greater than about 10:1,
preferably about 20:1- about 60:1. Preferred molecular sieves can include
BEA, MTW, FAU (including zeolite Y in both cubic and hexagonal forms, and
zeolite X), MOR, LTL, ITH, ITW, MEL, FER, TON, MFS, IWW, MFI, EUO, MTT,
HEU, CHA, ERI, MWW, and LTA. Preferably, the zeolite can be MFI and/or
MTW. Suitable zeolite amounts in the catalyst may range from about 1-
about 99%, and preferably from about 10- about 90%, by weight. The
balance of the catalyst can be composed of a refractory binder or matrix
that is optionally utilized to facilitate fabrication, provide strength,
and reduce costs. Suitable binders can include inorganic oxides, such as
at least one of alumina, magnesia, zirconia, chromia, titania, boria,
thoria, phosphate, zinc oxide, and silica.

[0038] Generally, the catalyst is essentially absent of at least one
metal, and typically includes less than about 0.1%, by weight, of total
metal based on the weight of the catalyst. Moreover, the catalyst
preferably has less than about 0.01%, more preferably has less than about
0.001%, and optimally has less than about 0.0001%, by weight, of total
metal based on the weight of the catalyst. Generally, the benzene
methylation zone 270 can provide the benzene methylation zone effluent
274, which can be utilized as a part of the stripper feed 196, as
discussed above.

[0039] Referring to FIG. 2, another exemplary aromatic production
apparatus 300 is depicted, and can be utilized in a similar facility and
produce similar products as the aromatic production apparatus 100. The
aromatic production apparatus 300 can include the extraction zone 150,
the transalkylation zone 180, the stripper zone 200, the fractionation
zone 220, and the sponge adsorption zone 250. Generally, these zones are
similar to those described above. In addition, the streams flowing to and
from these zones can be substantially similar as the streams described
above. In addition, the aromatic production apparatus 300 can also
include a first benzene methylation zone 320 and a second benzene
methylation zone 360.

[0040] Generally, a reformate feed 304 can be provided to the extraction
zone 150. The extraction zone 150 can provide a product stream 356 and a
raffinate stream 358. The raffinate stream 358 can exit the aromatic
production apparatus 300 and be used elsewhere in the refinery or
chemical manufacturing facility. Optionally, at least a portion of the
raffinate stream 358 can be directed to the first benzene methylation
zone 320.

[0041] The product stream 356 can be combined with a stripper bottom
stream 332, as hereinafter described, and form a feed 368 to the
fractionation zone 220. The fractionation zone 220 can include the
benzene fractionation zone 230 and the toluene fractionation zone 240.

[0042] The feed 368 can be provided to the benzene fractionation zone 230,
which in turn provides an overhead stream 370 including benzene, which
can be split into streams 372 and 374 as hereinafter described, and a
bottom stream 376 including one or more A7.sup.+ hydrocarbons. The bottom
stream 376 can be provided to the toluene fractionation zone 240. The
toluene fractionation zone 240 can provide a bottom stream 384 including
one or more A8.sup.+ aromatics. The bottom stream 384 can be provided to
any suitable zone, such as a para-xylene separation zone and an
isomerization zone for obtaining one or more desired products, as
described above. The overhead stream 380, including toluene, can be
provided to the transalkylation zone 180.

[0043] Generally, the transalkylation zone 180, as described above, can
provide a transalkylation zone effluent 308. The transalkylation zone
effluent 308 can be combined with the second benzene methylation zone
effluent 364, as hereinafter described, to form a stripper feed 312. In
an alternative embodiment, the transalkylation zone effluent 308 may be
provided to the first benzene methylation zone 320 and/or second benzene
methylation zone 360.

[0044] The stripper feed 312 can be provided to the stripper zone 200. The
stripper zone 200 can provide an overhead stream 330 and stripper bottom
stream 332. This overhead stream 330 may include one or more C3.sup.+
hydrocarbons due to dealkylation of one or more C9.sup.+ aromatics. The
stripper bottom stream 332 can be combined with the product stream 356 to
form the feed 368.

[0045] The overhead stream 330 can be combined with a fuel gas stream 306.
Generally, the fuel gas stream 306 can have the same composition as the
fuel gas stream 112, as described above. The streams 306 and 330 can form
a combined stream 310, which in turn can be combined with benzene from a
stream 372 split from the overhead stream 370. Thus, the sponge
adsorption zone 250 can include at least a portion of, independently, the
overhead stream 330, the fuel gas stream 306, and the stream 372 from a
fractionation zone 220. The streams 310 and 372 can in turn, be combined
to form a feed 390 for the sponge adsorption zone 250, as described
above. Alternatively, the streams 310 and 372 can be provided to and
mixed in the sponge adsorption zone 250.

[0046] The sponge adsorption zone 250 can provide a bottom stream 352 and
an overhead stream 354, which can include a fuel gas having a composition
substantially the same as the fuel gas stream 254, as described above.
Alternatively, the sponge adsorption zone 250 can be omitted and the feed
390 can be combined with the first benzene methylation zone effluent 324,
as described below.

[0047] Another portion 374 of the overhead stream 370 can be provided to a
first benzene methylation zone 320, operating similarly as the benzene
methylation zone 270 described above. In addition to receiving the
portion 374, the first benzene methylation zone 320 can also receive a C5
naphtha stream 316, including one or more C5 hydrocarbons. Usually, one
or more C5-C6 hydrocarbons are provided with benzene to the first benzene
methylation zone 320. Pentane can be provided from naphtha and/or a
depentanizer overhead stream. Optionally, the C5 naphtha stream 316 may
be split into multiple feed streams 318 and provided at multiple feed
points into the first benzene methylation zone 320. The C5 multipoint
injection of C5 hydrocarbons in the first benzene methylation zone 320
can maintain high benzene and pentane ratios. The first benzene
methylation zone 320 often includes a single reactor. Alternatively, the
stream 358 may optionally be combined with the stream 316 and provided as
a feed to the first benzene methylation zone 320.

[0048] Generally, the first benzene methylation zone 320 can provide a
first benzene methylation zone effluent 324 that can be combined with the
sponge adsorption zone bottom stream 352, which can include propane and
benzene. The streams 352 and 324 can form a combined feed 336, which is
passed through a heater 340, which can be any suitable heating device,
such as a furnace.

[0049] After being heated, a feed 344 can be provided to the second
benzene methylation zone 360 operating similarly as the benzene
methylation zone 270, as described above. Often, the second benzene
methylation zone 360 can provide a second benzene methylation zone
effluent 364, which can be combined with the transalkylation zone
effluent 308, as described above.

[0050] Generally, the second benzene methylation zone 360 operates at a
temperature of about 10- about 100° C., preferably about 20- about
80° C. higher than the first benzene methylation zone 320.
Typically, the first benzene methylation zone 320 operates at less severe
conditions using heavier hydrocarbons such as one or more C4.sup.+
alkanes. Additional one or more C3 hydrocarbons can be provided to the
first benzene methylation zone effluent 324 and fed to the second benzene
methylation zone 360. Although not wanting to be bound by theory, a
portion of the one or more C4.sup.+ alkanes can be converted to lighter
one or more C4.sup.- alkanes. The first benzene methylation zone effluent
324 may be provided to the second benzene methylation zone 360 at higher
severity where C4.sup.- alkanes may be more reactive. Optionally, the
first benzene methylation zone effluent 324 containing C3 hydrocarbons
can be alkylated with fresh propane in the second benzene methylation
zone 360 at an elevated temperature.

[0051] The first benzene methylation zone 320 can be operated to achieve
about 20- about 45%, by weight, benzene conversion to one or more
A7.sup.+ hydrocarbons, and about 60- about 100%, by weight, one or more
C4.sup.+ hydrocarbons conversion. Generally, the one or more C4.sup.+
alkanes can be converted to one or more A7.sup.+ alkyl groups, C4hydrocarbons, and C2.sup.- hydrocarbons. Usually, the one or more
C4.sup.+ alkanes selectivity to the one or more A7.sup.+ aromatics is at
least about 20%, by weight, preferably about 30%, by weight. Typically,
the one or more C4.sup.+ hydrocarbons selectivity to the one or more C3
hydrocarbons are about 25- about 50%, by weight. The second benzene
methylation zone 360 can be at an elevated temperature with a benzene
conversion of at least about 20%, by weight, preferably at least about
30%, by weight, conversion per pass. Usually at these conditions about
30- about 40%, by weight, of the C3 hydrocarbons converted are in the
form of one or more A7.sup.+ alkyl groups in the product. The overall
selectivity to one or more A7.sup.+ alkyl groups for the one or more
C4.sup.+ hydrocarbons may be about 30- about 50%, by weight, for zones
320 and 360. Generally, the one or more C4.sup.+ hydrocarbons conversion
to one or more A7.sup.+ alkyl groups is higher utilizing the two stages
in combination as disclosed herein when compared to the performance that
can be achieved using only the first benzene methylation zone 320.

[0052] As an example, the embodiments disclosed herein can achieve about
10- about 50%, by weight, increase in a xylene yield from the aromatic
production apparatus 100 by utilizing fuel gas and one or more C4.sup.+
alkanes. The two zones 320 and 360 may have C4.sup.+ hydrocarbon stream,
such as a higher raffinate or a light naphtha, selectivity to one or more
A7.sup.+ alkyl groups processing a light naphtha or raffinate only in a
first benzene methylation zone 320 without subsequent conversion of
propane in the second benzene methylation zone 360. Therefore, the
overall selectivity of alkylation can increase from about 25%, by weight,
with a first benzene methylation zone 320 and about 40%, by weight, with
a second benzene methylation zone 360.

[0053] In an alternative embodiment, the sponge adsorption zone 250 can be
positioned upstream of the first benzene methylation zone 320. The
conditions of the first benzene methylation zone 320 may be tailored so
that much of the one or more C3 hydrocarbons passes through largely
unreacted with substantial conversion of the C4.sup.+ hydrocarbons. The
effluent from the first benzene methylation zone 320 is provided to the
second benzene methylation zone 360, which can operate at higher
severity, i.e. higher temperature and/or lower pressure, to convert the
one or more C4.sup.- hydrocarbons. Although not wanting to be bound by
theory, the selectivity of the alkylating agent can be maximized in the
alkylation reaction with benzene and cracking of C1 or C2 hydrocarbons
may be minimized.

[0054] Without further elaboration, it is believed that one skilled in the
art can, using the preceding description, utilize the present invention
to its fullest extent. The preceding preferred specific embodiments are,
therefore, to be construed as merely illustrative, and not limitative of
the remainder of the disclosure in any way whatsoever.

[0055] In the foregoing, all temperatures are set forth in degrees Celsius
and, all parts and percentages are by weight, unless otherwise indicated.

[0056] From the foregoing description, one skilled in the art can easily
ascertain the essential characteristics of this invention and, without
departing from the spirit and scope thereof, can make various changes and
modifications of the invention to adapt it to various usages and
conditions.